This invention relates to a copier/printer apparatus, and more particularly to a sheet corrugation system for use in such an apparatus.
In an electrostatographic reproducing apparatus commonly in use today, a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the usual document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas in the photoconductive insulating area to form a powder image on the photoconductive area. This image may subsequently be transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image to a support surface, the photoconductive insulating member is cleaned of any residual toner that may remain thereon in preparation for the next imaging cycle.
Commercial applications of this apparatus have become increasing complex offering the users a variety of printing and copying options. One of the options of particular interest to a growing variety of customer applications is the capability for such machines to produce duplex prints and copies. By duplex copying or printing it is intended to define copies on which both sides of a single sheet are provided with fuser toner images. Another capability being provided in copying and printing machines with increasing frequency is that of being capable of providing two color or highlight color simplex, toner images on one side only of the copy or print. Both of these capabilities present significant problems in the handling of the copy substrates in an automatic printing or copying machine since the copy substrate on which the duplex image is formed or the second color or highlight color image is formed has already passed through the printing machine once to have the first toner image formed. In completing the first toner image the copy substrate is passed through a fuser which typically is at a temperature of about 400.degree. F. to thereby raise the temperature of the thermoplastic toner material to a level at which it will coalesce and penetrate into the substrate, typically the paper fibers. As a result of this heating which is also typically performed in a heated roll fuser using both heat and pressure between the fuser roll and a pressure roll, the copy substrates are subjected to sufficient stress that they have a slight amount of curl or other nonplanar deformity resulting in poor stacking between adjacent sheets. As a result, the first produced copy substrates having fused toner images thereon when collected in a duplex tray within the printing machine for subsequent duplex or second color reproduction do not stack the way virgin copy substrates stack but rather stack with nonuniform gaps or air pockets between adjacent copy substrates. This tendency of such copy substrates to fluff creates feeding difficulties in sheet feeders used to feed the copy substrates from the collection tray for the second pass through the printing or copying apparatus.
The problem of properly repeated restacking a series of documents one after another in a copier document stacking tray for duplexing purposes is much more than a problem in free fall dynamics. The trajectory of the documents must be controlled without damage or wearing the documents so that the documents consistently travel to and hit the proper landing area and stops flat in the aligned stack position so that they can be subsequently recaptured by the feeder and refed to be recirculated past the platen of the copier for copying at the proper position (alignment) on the platen. Document sheet restacking is affected by factors including especially the sheet's release point, cantilever (unsupported length), velocity, mass, stiffness, and "air foil" shape including both induced and accidental curls on one or both axis of the sheet. Original documents are typically flimsy sheets which easily and typically change shape when released for restacking from air resistance, air flow lift, preset curl tendencies, etc. All of these characteristics affect the "flight" of the document being restacked and its settling position. The restack trajectory problem also applies to copies directed to a duplex tray for refeeding in order to receive second side images.
Attempts at answering the heretofore mentioned curl problems when feeding copy sheets as well as documents have resulted in the development of a particular sheet feeder in U.S. Pat. No. 4,901,117 and a document restacking system in U.S. Pat. No. 4,469,319 that includes automatic variable corrugation stacking means in the form of flexible deflector tabs and flexible finger-like members.
Other patents of interest include U.S. Pat. No. 4,842,263 which discloses a sheet reversing apparatus which employs a buckle chamber and input and output rollers which, together with a common roller, serve to form input and output nips for conveying a sheet into and out of the buckle chamber to reverse the lead and trail edge orientation thereof. The trail edge of the sheet is urged forward to become engaged by foam rollers which transfer the sheet from the input nip to the output nip.
U.S. Pat. No. 4,640,409 discloses a conveyor device for conveying sheet material by utilizing two pairs of parallel conveyor rollers, each pair including a deformable and a non-deformable roller. The deformable rollers are provided with a soft covering of rubber which increases the frictional property of the rollers to increase the speed of the fed sheets. The degree of deformation is dependent on the stiffness of the sheets passing through the rollers.
U.S. Pat. No. 4,767,114 discloses a sheet feeder which has a slip preventing mechanism consisting of a deformable member whose tip projects from a drive discharge roller and bends in contact with a sheet to be discharged and forcibly discharges the sheet into a small area. Transfer is conveniently attained without having the ink smearing or staining the transferred sheet.
U.S. Pat. No. 3,929,327 discloses a document transport and registration apparatus comprising an idler roller and a frusto-conical drive roller which cooperate with one another to advance a document along a pre-determined path. The cone shaped drive roller is flexible so that it may radially deform when advancing the document, whereby a misaligned sheet is automatically brought into alignment with a guide edge.
U.S. Pat. No. 4,893,806 discloses a pinch roller device to be used in automatic teller machines which eliminates misfeeding of deposit envelopes. A pinch roller is located between frame members above a foam-like drive roller for a conveyor belt. The pinch roller serves to provide pressure to the foam roller so that slack is eliminated and even bulky envelopes can be properly fed through the conveyor belts.
U.S. Pat. No. 4,831,416 discloses a sheet advancing apparatus for an electrophotographic printing machine in which a rotatably mounted member cooperates with a rotatably mounted polyhedron which creates a nip through which sheets are fed. Transport rolls are made from foam so light-weight and heavy copies can be easily conveyed forward. The rolls provide the correct amount of pressure to different thickness sheets by virtue of their composition. This arrangement improves the prior art where rigid transport rolls are spring mounted to resiliently urge the sheets forward.
All of the above-mentioned references are included herein by reference.
While some of the above-mentioned patents do eliminate some of the unwanted curl in sheets that are to be duplexed, as well as, original documents, that are to be recirculated, they are not entirely satisfactory.